1. Field of the Invention
The present invention relates to a control system for an automatic transmission mounted in a vehicle or the like. More specifically, the present invention relates to a control system for an automatic transmission capable of executing an automatic shift mode that performs automatic shifting based on a vehicle running state and also capable of executing a manual shift mode that performs shifting based on a command generated by manual operation.
2. Description of the Related Art
An automatic transmission mounted in a vehicle or the like is structured so as to automatically determine a speed ratio (shift speed) based in particular on an accelerator opening and a vehicle speed while the vehicle is traveling forward, and also achieve travel at a suitable speed ratio without requiring a shift operation from a driver. However, in response to recent demands for sporty driving, finer selection of an engine brake, and the like, a device has been proposed that enables a so-called manual shift operation, where the driver can freely select the speed ratio (shift speed). (See Japanese Patent Application Publication No. JP-A-H10-324169.)
With regard to stepped automatic transmissions in recent years, multi-stage automatic transmissions such as those achieving six or more forward speeds are now becoming mainstream in order to contribute to improved vehicle fuel economy and so forth. Even automatic transmissions that perform stepless shifting such as a belt type CVT now have segmented speed ratios (such as six or more speeds) and are structured so as to enable the selection of pseudo shift speeds.
However, when an automatic transmission is set with its speed ratios (shift speeds) segmented (multi-staged) in this manner, the speed ratio (shift speed) must be changed by, for example, two or three steps in order to attain significant engine braking during such times as downhill driving and sudden braking. Especially in cases where the above manual shift operation is performed, the driver may need to successively perform a number of manual shift operations in a short time. Such operations become a burden, leading to the problem of poor vehicle drivability.
When performing the above manual shift operation, the burden of the operation can conceivably be reduced with a configuration where a multi-stage change command can be performed by continuously pressing an operation lever or the like to a downshift command position, that is, by a so-called holding operation. However, considering a holding time for determination that must be set to ensure an erroneous operation or the like is not made, the shift command takes longer to complete and results in a poor response particularly ill-suited for sporty driving. In addition, the shift command ultimately increases one speed at a time, i.e., the automatic transmission is shifted one speed at a time, for example, from sixth speed to fifth to fourth and then to third. As a consequence, shifting is performed in succession and leads to the problem of poor drivability.